1. Field of the Invention
The present invention relates to an oil ring of metal periphery type oil seal and, more particularly, to an oil seal having at its outer peripheral portion a metallic reinforcer ring adapted to be fitted to a stationary part such as a housing of a machine and at its inner peripheral portion a rubber lip adapted for making a sliding contact with a rotary shaft.
2. Description of the Prior Art
Oil seals have been widely used as shaft seal device for preventing working oil or lubricating oil from leaking outside through a rotary shaft portion of hydraulic pump, bearing box and so forth. Various types of oil seals have been proposed and used in accordance with condition of use.
Among these oil seals, an oil seal of a type called metal periphery type oil seal is suitably used for sealing oil of a comparatively high pressure as in the case of hydraulic machines.
This type of oil seal has an outer peripheral reinforcement ring made of a metal and adapted to be fixedly fitted to a stationary part such as housing. Since the housing is usually made of a metal, a metal fit is achieved between the reinforcement ring and the housing to present a high fitting strength to withstand a high pressure.
This metal fit, however, requires a high precision of the fitting parts of these two metallic members. For this reason, the reinforcement ring is shaped by a precise and minute drawing die or the outer peripheral surface of the same is polished. If an axial scratch or the like damage is caused on the outer surface of the reinforcement ring due to friction or the like during fitting, the oil may undesirably leak through such a scratch or damage.
As a countermeasure for overcoming this porblem, it has been proposed to apply a rubber coating such as a sealant to the outer peripheral surface of the reinforcment ring. This countermeasure, however, requires an increased number of steps and incurs a rise of the cost.
The reinforcement ring of the metal periphery type oil seal has a substantially L-shaped section, one side portion of which constitutes the outer periphery of the oil seal while the other constituting the side part at the inner end of which attached is a rubber lip.
In this type of reinforcement ring, only one bend is provided between two sides of L-shape of the section. With such a sectional shape, it is necessary to increase the thickness of the reinforcement ring in order that the ring can withstand the stress which is generated therein when the ring is fitted to the housing.
In order to improve the strength of the reinforcement ring, it may be bent inwardly at an outer peripheral edge. If, however, the bent portion has a small radius of curvature no satisfactory increment of the strength would result.
In the metal periphery type oil seal of the kind described, it is also required to provide as large contact area as possible between the reinforcement ring and the housing, in order to ensure a tight fit therebetween to obtain a sufficient fitting strength and to prevent the leak of oil therethrough. For these reasons, the radius of curvature of the bend between two sides of the L-shaped section of the reinforcement ring is usually selected small. Such a small radius of curvature, however, causes a stress concentration which in turn requires an increment of thickness of the reinforcement ring.
The increase of the ring thickness incurs not only a difficulty in processing but also an increase in weight of the oil seal as a whole.
In the metal periphery type oil seal, a rubber member shaped integrally with the rubber lip is secured by baking to the entire inner surface of the reinforcement ring having the L-shaped section, in order to securely attach the lip to the metallic reinforcement ring.
In case of rubber periphery type oil seal, the rubber constituting the outer peripheral portion of the oil seal occupies about 1/3 of the whole seal, so that an uneconomically large amount of rubber is required to incur a material cost, although the problem concerning the oil leak at the outer periphery is less severe.